It is known to add a foaming agent to thermoplastics from U.S. Pat. Nos. 2,964,794; 3,268,636; 3,277,029; 3,290,261; 3,377,296; 3,436,446 and British patent 838,824. From U.S. patents 3,304,282; 3,396,142; 3,408,225; 3,437,632; 3,671,487 and 3,678,079, it is known to prepare glass fiber reinforced thermoplastics. Also, U.S. Pat. No. 3,334,154 discloses a polymer composition employing a flame-retardant additive comprising a copolymer. However, none of these references discloses a process for producing a foamed thermoplastic composition which comprises blending a minor amount of a foaming agent with the thermoplastic resin in an extruder and comminuting the resultant extrudate.
It has been discovered that a foamed thermoplastic composition is prepared by blending a minor amount of a foaming agent with a thermoplastic resin in an extruder and comminuting the resulting extrudate into foamed pellets or other suitable shapes. Thus, a foamed pellet, for example, is produced which does not require the use of additional foaming agent prior to molding and can be fed into a standard injection molding machine to produce a foamed part directly.